Some functions are flagged as not tail-recursive. A tail-recursive
function uses constant stack space, while a non-tail-recursive function
uses stack space proportional to the length of its list argument, which
can be a problem with very long lists. When the function takes several
list arguments, an approximate formula giving stack usage (in some
unspecified constant unit) is shown in parentheses.

The above considerations can usually be ignored if your lists are not
longer than about 10000 elements.

let length: list('a) => int;

Return the length (number of elements) of the given list.

let hd: list('a) => 'a;

Return the first element of the given list. Raise
Failure "hd" if the list is empty.

let tl: list('a) => list('a);

Return the given list without its first element. Raise
Failure "tl" if the list is empty.

let nth: (list('a), int) => 'a;

Return the n-th element of the given list.
The first element (head of the list) is at position 0.
Raise Failure "nth" if the list is too short.
Raise Invalid_argument "List.nth" if n is negative.

let rev: list('a) => list('a);

List reversal.

let append: (list('a), list('a)) => list('a);

Catenate two lists. Same function as the infix operator @.
Not tail-recursive (length of the first argument). The @
operator is not tail-recursive either.

let rev_append: (list('a), list('a)) => list('a);

List.rev_append l1 l2 reverses l1 and concatenates it to l2.
This is equivalent to List.rev l1 @ l2, but rev_append is
tail-recursive and more efficient.

let concat: list(list('a)) => list('a);

Concatenate a list of lists. The elements of the argument are all
concatenated together (in the same order) to give the result.
Not tail-recursive
(length of the argument + length of the longest sub-list).

let flatten: list(list('a)) => list('a);

Same as concat. Not tail-recursive
(length of the argument + length of the longest sub-list).

partition p l returns a pair of lists (l1, l2), where
l1 is the list of all the elements of l that
satisfy the predicate p, and l2 is the list of all the
elements of l that do not satisfy p.
The order of the elements in the input list is preserved.

Association lists

let assoc: ('a, list(('a, 'b))) => 'b;

assoc a l returns the value associated with key a in the list of
pairs l. That is,
assoc a [ ...; (a,b); ...] = b
if (a,b) is the leftmost binding of a in list l.
Raise Not_found if there is no value associated with a in the
list l.

let assq: ('a, list(('a, 'b))) => 'b;

Same as List.assoc, but uses physical equality instead of structural
equality to compare keys.

let mem_assoc: ('a, list(('a, 'b))) => bool;

Same as List.assoc, but simply return true if a binding exists,
and false if no bindings exist for the given key.

let mem_assq: ('a, list(('a, 'b))) => bool;

Same as List.mem_assoc, but uses physical equality instead of
structural equality to compare keys.

let remove_assoc: ('a, list(('a, 'b))) => list(('a, 'b));

remove_assoc a l returns the list of
pairs l without the first pair with key a, if any.
Not tail-recursive.

let remove_assq: ('a, list(('a, 'b))) => list(('a, 'b));

Same as List.remove_assoc, but uses physical equality instead
of structural equality to compare keys. Not tail-recursive.

Lists of pairs

let split: list(('a, 'b)) => (list('a), list('b));

Transform a list of pairs into a pair of lists:
split [(a1,b1); ...; (an,bn)] is ([a1; ...; an], [b1; ...; bn]).
Not tail-recursive.

let combine: (list('a), list('b)) => list(('a, 'b));

Transform a pair of lists into a list of pairs:
combine [a1; ...; an] [b1; ...; bn] is
[(a1,b1); ...; (an,bn)].
Raise Invalid_argument if the two lists
have different lengths. Not tail-recursive.

Sorting

let sort: (('a, 'a) => int, list('a)) => list('a);

Sort a list in increasing order according to a comparison
function. The comparison function must return 0 if its arguments
compare as equal, a positive integer if the first is greater,
and a negative integer if the first is smaller (see Array.sort for
a complete specification). For example,
Pervasives.compare is a suitable comparison function.
The resulting list is sorted in increasing order.
List.sort is guaranteed to run in constant heap space
(in addition to the size of the result list) and logarithmic
stack space.

The current implementation uses Merge Sort. It runs in constant
heap space and logarithmic stack space.

let stable_sort: (('a, 'a) => int, list('a)) => list('a);

Same as List.sort, but the sorting algorithm is guaranteed to
be stable (i.e. elements that compare equal are kept in their
original order) .

The current implementation uses Merge Sort. It runs in constant
heap space and logarithmic stack space.

Merge two lists:
Assuming that l1 and l2 are sorted according to the
comparison function cmp, merge cmp l1 l2 will return a
sorted list containting all the elements of l1 and l2.
If several elements compare equal, the elements of l1 will be
before the elements of l2.
Not tail-recursive (sum of the lengths of the arguments).